If one checksum is supplied to a SRC_URI, we really don't want to show
warnings about the other type which isn't present as one checksum
is really good enough for most cases.
(Bitbake rev: 43358a9b595b2928458a5f463cf1949394160c3a)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>